3.自动配置控制器以及扫描控制器的原理，核心注解

3.1.如何自动配置Spring+SpringMVC

3.1.1.原理

      Spring Boot在进行SpringApplication 对象实例化是会加载META-INF/spring.factories文件，将该配置文件中的配置载入到Spring容器，进行自动配置。

3.1.2.源码分析 

 

 

 

    

以是视图转换器为例

<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
　　<property name="prefix" value="/WEB-INF/html/" />
　　<property name="suffix" value=".html" />
　　<property name="order" value="2"/>
</bean>

 org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration

在项目查找 Ctrl+Shift+T 查找"类":WebClientAutoConfiguration

在application.properites配置

前缀名

spring.mvc.view.prefix = /WEB-INF/jsp/

后缀名

spring.mvc.view.suffix=.jsp

 

3.2.如何扫描控制器的

 原理：当启动App.java时，SpringBoot 会议App.java为基准点依次向上扫描同一级的包也就是controller包以及其子包内控制器，或者数据访问接口

，@Service，@Component等。

 

3.3.Spring Boot的核心注解

3.3.1.启动类与@SpringBootApplication

Spring Boot的项目一般都会是有注解*application标注的入口类，入口类中会有main方法，main方法是一个标准的JAVA应用程序的入口方法，可以直接启动。

   @SpringBootApplication 注解是Spring Boot的核心注解，以此注解标注的入口类是应用的启动类，通常会在启动类的main方法中通过SpringApplication.run(App.calss,args)

   来起到Spring Boot应用项目。

  

@SpringBootApplication
public class App 
{
    public static void main( String[] args )
    {
        System.out.println( "Hello World!" );
        //启动Spring Boot的核心代码
        SpringApplication.run(App.class, args);
    }
}

@SpringBootApplication源码

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
        @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return the classes to exclude
     */
    @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "exclude")
    Class<?>[] exclude() default {};

    /**
     * Exclude specific auto-configuration class names such that they will never be
     * applied.
     * @return the class names to exclude
     * @since 1.3.0
     */
    @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "excludeName")
    String[] excludeName() default {};

    /**
     * Base packages to scan for annotated components. Use {@link #scanBasePackageClasses}
     * for a type-safe alternative to String-based package names.
     * @return base packages to scan
     * @since 1.3.0
     */
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
    String[] scanBasePackages() default {};

    /**
     * Type-safe alternative to {@link #scanBasePackages} for specifying the packages to
     * scan for annotated components. The package of each class specified will be scanned.
     * <p>
     * Consider creating a special no-op marker class or interface in each package that
     * serves no purpose other than being referenced by this attribute.
     * @return base packages to scan
     * @since 1.3.0
     */
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
    Class<?>[] scanBasePackageClasses() default {};

}

SpringBootConfiguration的源码
这是Spring Boot项目的配置注解，这也是一个组合注解：
在Spring Boot项目中推选使用@SpringBootConfiguration注解来替代@Configuration注解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {

}

3.3.2.@EnableAutoConfiguration

启动自动配置，该注解会让Spring Boot根据当前项目所依赖的JAR包自动配置项目的相关的配置项

 

3.3.3.@ComponentScan

  扫描配置，Spring Boot默认扫描@SpringBootApplication所在类的同级包以及他的子包，

          所以建议将@SpringBootApplication修饰的入口类放置在项目包下（Group Id+ArtifactId）可以保证SpringBoot项目启动时扫描所有的包

 

3.3.4.关闭自动配置

  如何关闭自动配置那？

　　通过查看@SpringBootApplication的源码可以看出，关闭特定的自动配置应该使用@SpringBootApplication下的exclude参数，现在已关闭Redis自动配置为例：

   @SpringBootApplication(exclude={RedisAutoConfiguration.class})